ASHs: application-specific handlers for high-performance messaging

Application-specific safe message handlers (ASHs) are designed to provide applications with hardware-level network performance. ASHs are user-written code fragments that safely and efficiently execute in the kernel in response to message arrival. ASHs can direct message transfers (thereby eliminating copies) and send messages (thereby reducing send-response latency). In addition, the ASH system provides support for dynamic integrated layer processing (thereby eliminating duplicate message traversals) and dynamic protocol composition (thereby supporting modularity). ASHs offer this high degree of flexibility while still providing network performance as good as, or (if they exploit application-specific knowledge) even better than, hard-wired in-kernel implementations. A combination of user-level microbenchmarks and end-to-end system measurements using TCP demonstrates the benefits of the ASH system     

A comparison of two paradigms for distributed shared memory

Two paradigms for distributed shared memory on loosely-coupled computing systems are compared: the shared data-object model as used in Orca, a programming language specially designed for loosely-coupled computing systems, and the shared virtual memory model. For both paradigms two systems are described, one using only point-to-point messages, the other using broadcasting as well. The two paradigms and their implementations are described briefly. Their performances are compared on four applications: the travelling-salesman problem, alpha-beta search, matrix multiplication and the all-pairs shortest-paths problem. Measurements were obtained on a system consisting of 10 MC68020 processors connected by an Ethernet. For comparison purposes, the applications have also been run on a system with physical shared memory. In addition, the paper gives measurements for the first two applications above when remote procedure call is used as the communication mechanism. The measurements show that both paradigms can be used efficiently for programming large-grain parallel applications, with significant speed-ups. The structured shared data-object model achieves the highest speed-ups and is easiest to program and to debug.     

The role of glycoproteins gC, gE, gI, and gG in the induction of cell-mediated immune responses to bovine herpesvirus 1

Mutant viruses with deletions in genes encoding non-essential glycoproteins are considered as promising bovine herpesvirus 1 (BHV1) vaccine candidates. The present study compared the influence of various gene deletions (gC, gE, gI, gG) on the induction of cell-mediated immune responses against the virus. The highest BHV1 specific lymphoproliferative response was observed in the group of calves inoculated with the gC- mutant. However, in all groups of inoculated calves, limiting dilution analysis showed marked individual variability in the number of BHV1 specific T lymphocytes that were stimulated. The same animals were then challenged with wild-type BHV1. In these animals, limiting dilution analysis did not reveal gE, gI nor gG as a major T lymphocyte antigen. However, further analysis suggested the T cell antigenicity of gE in a low number of BHV1 hyperimmunized calves. Stimulation of MHC unrestricted cytotoxicity was also evaluated after inoculation with the various deletion mutants. Cytotoxicity in gC- inoculated calves was as high as in BHV1 inoculated calves. In conclusion, among the BHV1 deletion mutants that were tested, the gC- mutant stimulated the best cell-mediated immune responses.     

A frequency response function for linear,time-varying systems

It is well known that the steady-state response of a linear, time-invariant, finite-dimensional, exponentially stable system to a periodic input signal results, after a phase shift, in a periodic output signal of the same period with amplitude equal to the rescaling of the input amplitude by the modulus of the value of the transfer function at the given frequency. Moreover, the phase shift of the output signal is equal to the phase of the value of the transfer function at the given frequency. For this reason the transfer function is also referred to as the frequency response function. We present an analogue of this idea for linear, finite-dimensional, time-varying systems, in both the continuous- and discrete-time settings. The problem of constructing a time-varying system which associates a given output signal to each complex exponential input signal in a prescribed set can be posed as a modeling question. This leads to a new modeling interpretation for some of the time-varying interpolation problems which have recently been studied in the literature and a new motivation for the study of point evaluation for triangular operators recently introduced by Alpay, Dewilde, and Dym and by the authors for the continuous-time case.The first author was partially supported by NSF Grant 9500912.     

On minimality in the partial realization problem

A compression algorithm is constructed which allows one to reduce an arbitrary realization of a finite sequence of matrices M₁,…, M_r to a minimal partial realization of M₁,…, M_r. Furthermore, a state space criterion of minimality of a partial realization and a formula for the minimal state space dimension are obtained.     

Building reliable mobile‐aware applications using the Rover toolkit

This paper discusses extensions to the Rover toolkit for constructing reliable mobile‐aware applications. The extensions improve upon the existing failure model, which addresses client or communication failures and guarantees reliable message delivery from clients to server, but does not address server failures (e.g., the loss of an incoming message due to server failure) (Joseph et al., 1997). Due to the unpredictable, intermittent communication connectivity typically found in mobile client environments, it is inappropriate to make clients responsible for guaranteeing request completion at servers. The extensions discussed in this paper provide both system‐ and language‐level support for reliable operation in the form of stable logging of each message received by a server, per‐application stable variables, programmer‐supplied failure recovery procedures, server process failure detection, and automatic server process restart. The design and implementation of fault‐tolerance support is optimized for high performance in the normal case (network connectivity provided by a high latency, low bandwidth, wireless link): measurements show a best‐case overhead of less than 7% for a reliable null RPC over wired and cellular dialup links. Experimental results from both micro‐benchmarks and applications, such as the Rover Web Browser proxy, show that support for reliable operation can be provided at an overhead of only a few percent of execution time during normal operation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Parallel programming using shared objects and broadcasting

The two major design approaches taken to build distributed and parallel computer systems, multiprocessing and multicomputing, are discussed. A model that combines the best properties of both multiprocessor and multicomputer systems, easy-to-build hardware, and a conceptually simple programming model is presented. Using this model, a programmer defines and invokes operations on shared objects, the runtime system handles reads and writes on these objects, and the reliable broadcast layer implements indivisible updates to objects using the sequencing protocol. The resulting system is easy to program, easy to build, and has acceptable performance on problems with a moderate grain size in which reads are much more common than writes. Orca, a procedural language whose sequential constructs are roughly similar to languages like C or Modula 2 but which also supports parallel processes and shared objects and has been used to develop applications for the prototype system, is described     

Chord: a scalable peer-to-peer lookup protocol for Internet applications

A fundamental problem that confronts peer-to-peer applications is the efficient location of the node that stores a desired data item. This paper presents Chord, a distributed lookup protocol that addresses this problem. Chord provides support for just one operation: given a key, it maps the key onto a node. Data location can be easily implemented on top of Chord by associating a key with each data item, and storing the key/data pair at the node to which the key maps. Chord adapts efficiently as nodes join and leave the system, and can answer queries even if the system is continuously changing. Results from theoretical analysis and simulations show that Chord is scalable: Communication cost and the state maintained by each node scale logarithmically with the number of Chord nodes.